1. Field of the Invention
This invention relates to a color filter to be employed in a liquid crystal device, a solid-state image pickup device, etc., and to a liquid crystal display device which is provided with such a color filter.
2. Description of the Related Art
Recently, because of thinness in wall thickness and the resultant advantages such as space-saving, lightweight properties, power-saving, etc., a liquid crystal display device is now rapidly propagated especially as a display device for television. In order to make the liquid crystal display device applicable to television, it is required to further enhance various properties such as the brightness, contrast and omnidirectional visibility, so that the display device is now frequently constructed such that an optical retardation control layer is employed in combination with a linear deflecting plate.
In recent years in particular, in the case of a vertical orientation mode liquid crystal display which is capable of exhibiting a display of high contrast, there has been employed an optical retardation film (or negative C plate) exhibiting negative birefringence anisotropy and having the optical axis perpendicular to the substrate together with an optical retardation film (or positive A plate) exhibiting positive birefringence anisotropy and having the optical axis horizontal to the substrate (for example, see JP-A 10-153802).
As for specific examples of these optical retardation films, there have been generally employed those that can be obtained by stretching an polycarbonate film or that can be obtained by coating a liquid crystal material exhibiting birefringence anisotropy on the surface of triacetyl cellulose film, etc.
However, in the case of the aforementioned optical retardation films, since the magnitude of retardation thereof is uniformly retained in-plane and hence the magnitude of retardation is not optimally set for each of pixels to be actually displaced, it cannot necessarily be said that the optical retardation compensation is optimally executed by the optical retardation films.
One of the reasons is that since the optical retardation and refractive index of liquid crystal themselves are dependent on the wavelength of transmitting light, the magnitude of retardation demanded for the optical retardation film may differ depending on the color of each pixel constituting the color filter (actually, on the wavelength of transmitting light). In view of this, for example, JP-A 2005-148118 discloses the following proposal. Namely, according to this document, the retardation is controlled depending on the wavelength of transmitting light, thereby making it possible to optimize the compensation of optical retardation.
Another reason is that when each of color pixels constituting the color filter has in itself a perpendicular (thickness-wise) optical retardation, optical retardation is generated in transmitting light, so that the viewing-angle dependence of liquid crystal display device becomes larger, thereby deteriorating the display characteristics thereof. In view of this, for example, JP-A 2000-136253 discloses the following proposal. Namely, according to this document, a colored polymer thin film is constructed so as to contain a macromolecule having a planar structure group on its side chain or so as to contain birefringent-reducing particles having a birefringence index which is opposite in sign (positive or negative) to the macromolecule, thereby trying to reduce the magnitude of retardation which the color filter has.
As a matter of fact however, in spite of these proposals, there is a problem that when black color in normally-black operation to which viewing-angle compensation has been applied is observed obliquely, the black color appears colored into reddish purple due to the light leakage of red and blue.
As a result of studies made by the present inventors on this problem, it has been found out that the perpendicular optical retardation of each of red, green and blue pixels constituting the color filter differs from each other. For example, it has been found out that, in the case of the color filter to be manufactured by making use of a pigment dispersion type color composition, a green pixel exhibits a large magnitude of negative retardation as compared with red and blue pixels. Since the magnitude of retardation of color filter is relatively small as compared with that of other components to be employed in a liquid crystal display device, the aforementioned problem was not considered seriously to date. However, since the optical design is now generally performed centering around green, if the magnitude of retardation of green pixel differs greatly from that of red and blue pixels, light leakage is generated, thus raising problems with respect to the viewing-angle visibility of the display device.